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I have a TS-830S that was initially doing about 60W in CW at 10m and 70W at 40m. I've heard these things are capable of at least 100W.

Determined, I started doing research on what components to look at in addition to the tubes. I'm able to get ALC with CAR at 5 on 40 and 8 on 10 meters- so I think the drive is sufficient. This lead me to suspect the final tubes.

Before getting a pricey set of tubes- I tried some of the cheaper avenues. I have replace the C7 C8 and L1 components of the final cage with a kit from hybridrestore.com. Next- I replaced the cathode and screen resistors with another kit from the same vendor.

I didn't get much power out of that- but I did notice the tubes we easier to neutralize. I use an SDR running SDR# as my second receive and tune to a dip in signal strength with SG.SW OFF. The dip was much sharper and more pronounced- but it could have been placebo.

Finally I decided to try new tubes. I got a pair of NOS tubes from an ebay vendor with lots of good rep. I put them in the radio and "cooked" the getters a bit- maybe 5 minutes- with the SG switch off. Clearly that wasn't long enough, because a tube arched and the resistors went out of spec.

I found some 1/2W metal film resistors on ebay in 100ohm and 20ohm for replacement. And this time cooked the getters for a good hour.

Things appear to be working. And I'm getting about 90W on 40m and 80W on 20m. But I want to get more out of it.

I understand that the power differences here are negligible. This is more for my satisfaction of getting and old rig running at peak performance again.

My question is- what would you suspect next? Maybe the tubes are not quite "NOS" as claimed? Should I try newly manufactured Chinese tubes that haven't been sitting on the shelf for 30 years? Should I replace the HV caps? I'm getting an 800V reading on the HV meter. Anything else to look at next?

rclocher3
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Paul
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    What setup and equipment are you using to measure the Po? – Glenn W9IQ Jul 25 '18 at 16:04
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    I've got an MFJ-894 sitting between the rig and an MFJ-260C dummy load. Jumpers all under a foot. Readouts in power look the same if I use a real dipole antenna instead of the dummy load. I just have about 1.5 swr in that case. – Paul Jul 25 '18 at 17:33
  • What is the the grid voltage, the screen voltage, and the key-down idling current with no output? – Mike Waters Jul 25 '18 at 18:04
  • How would I measure that? I assume it's different from the HV meter on the radio. And would a basic AC/DC multimeter work? Bias current in SSB mode with mic gain at 0 is 60mA. – Paul Jul 25 '18 at 18:05
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    Hi Paul, I hope you don't mind but I edited your title to be less model-specific, because surely lots of other people out there with other rigs with tube finals are also having trouble getting full rated output power. In other words, I hope I made your question a little more useful to others. – rclocher3 Jul 25 '18 at 18:59
  • Those voltages are measured at the 6146B sockets on the underside of the chassis. But it sounds like you are unfamiliar with the procedure. Can you get someone who is to help you? – Mike Waters Jul 25 '18 at 19:16
  • I don't know anyone who's familiar with tube rigs. I've worked on that board with the sockets though (when soldering in new resistors) and the pins are numbered. Just not sure what equipment would be needed. – Paul Jul 25 '18 at 20:33
  • You are probably within the limits of the accuracy of the MFJ meter unless you have calibrated it. – Glenn W9IQ Jul 25 '18 at 21:43
  • by the way, you don't have to (and should not, in fact) resort to ebay to get normal components like wired 1/2 W resistors in standard values, or high-voltage capacitors; you can buy these cheap, with guarantees, quick delivery from large electronic distributors (digikey, mouser, arrow, quite a few others)! Ebay's really not the place for basic components. – Marcus Müller Jul 26 '18 at 08:20
  • @MarcusMüller i initially took a look at mouser but got overwhelmed by all the choices. the shipping is more than the cost of the few components i needed as well. what do you think of these? the part of the data sheet that caught my eye was "low noise" and "excellent HF characteristics". does that mean low inductance? https://www.mouser.com/datasheet/2/427/cmfind-239942.pdf – Paul Jul 26 '18 at 14:36
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    Ah, hadn't tought of the shipping cost/item value problem. However, if you're in the US, arrow.com is currently offering free next-day shipping, so maybe that's more to your taste. Regarding "HF characteristics": for metal film resistors, just don't worry about the inductivity south of 1GHz; these aren't wirewounds! I'd expect the leads of the resistor to have more inductance than the resistor itself, and you can't do much about that. – Marcus Müller Jul 26 '18 at 16:29
  • @MikeWaters figured out what you meant ( I think ).

    Looking at the final unit schematic, pin 5 on the socket goes to what appears to be the Grid (Grid 1) on the tubes. I got a voltage of about -93V. Pin 5 goes to Grid 2 (usually the screen grid on pentodes?) and has a voltage of about 233V. Plate voltage is about 860V.

     – Paul Aug 08 '18 at 02:10
  • Now the next step is to look at the tube data sheet and see if those voltages are within tolerance for the class of operation. – Mike Waters Aug 08 '18 at 02:15
  • And check the filament voltage as well. – Mike Waters Aug 08 '18 at 13:24
  • @MikeWaters I'm a little confused by what I'm seeing in the datasheet. The max for class AB1 ICAS has a DC plate voltage of 750V. The schematic shows a voltage of 900V. Are these tubes being overworked by Kenwood?

    Grid #2 voltage is 250V max. Grid #1 specifies -48V.

     – Paul Aug 09 '18 at 14:18

1 Answers1

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As a KWM-2 overhauler, I'm impressed with your knowledgeable attack on the problem. Two suggestions:

I would look at the driver stage, and check voltages and the cathode and screen resistors (like you did for the finals) to make sure their output is up to spec.

If you want meaningfully more output, an easy way is to get an amplifier in the 500 Watt class, such as a 30L1, can be had for short money. Makes a huge difference in the quality of on-air conversation.

By the way, gettering generally takes of the order of 24 hours. Time well spent, as you found out the hard way.

73

Ted
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